Seat suspension mats form the inner supporting structure of seats. This supporting structure supports the actual soft cushioning of the seat in a resilient manner. In seats of motor vehicles, suspension mats are usually connected to a rigid seat frame.
Such suspension mats are known, e.g. from EP 1 780 076 A1. The described suspension mat comprises lateral wire elements and a plurality of transverse wires. Some of transverse wires extend beyond the lateral wire elements to terminate in hook-like shaped ends. The hooks are used for mounting the suspension mat to a seat frame. Particularly, the hooks are hooked onto the seat frame. A common configuration of a suspension mat hooked into a seat frame is shown in FIG. 1 for the backrest a motor vehicle seat.
The transverse wires and the seat frame are both usually made of metal. Therefore, when force is exerted on the suspension mat, the hooks may chafe on the seat frame, thereby producing abrasion and noise. To avoid this disadvantage it is known to coat or to overmould such hooks with plastic material. However, such a coating by a kind of paint or an overmoulding in an injection moulding process is complicated and expensive.
To avoid such drawbacks the EP 1 780 076 A1 teaches to coat such hooks with a hollow plastic tube. This coating helps to prevent the noise and vibration problems. However, applying this hollow plastic tube requires pushing such plastic tube onto the initially straight end of a transverse steel wire and subsequently bending the straight end together with the hollow plastic tube. Because of the different materials, i.e. steel of the wire and plastic material of the tube, this bending process leads to heavy compression stresses on the tube which may damage the tube. Particularly, when a small bending radius of the hook is required the plastic tube is likely to be damaged or deformed during bending. This causes on the one hand mounting problems and on the other a risk of a metal to metal contact of seat frame and hook which leads to abrasion and noise.
In view of the above, it is an object of the present invention to provide a suspension mat which can be mounted to a seat frame without the danger of generation of noise and without excessive stresses and risk of damaging of the tube during the manufacturing process and use. Further, another object of the invention is to provide a manufacturing method and corresponding apparatus that avoids the above mentioned drawbacks of damaging the coat of the hooks.